Bucking trigger circuit



ch 3 1950 R. L. PALMER 2,524,134

BUCKING TRIGGER CIRCUIT Filed July 9, 1948 OUTPUT FEM/NHL 2'5 INVENTORAmp 4. 94mm Patented Oct. 3, 1950 BUCKING TRIGGER CIRCUIT Ralph L.Palmer, Poughkeepsie, N. Y., assignor to International Business MachinesCorporation, New York, N. Y., a corporation of New York Application July9, 1948, Serial No. 37,939

This invention relates to trigger circuits and more particularly totriggers of the type having two grid controlled tubes and two stableconditions alternately assumed.

In such triggers it is conventional to connect the plate of each tube tothe control grid of the other through a resistor and capacitor in shunt.The stable condition of the trigger is switched by the application ofpulses to either or both control grids or to either or both plates. Assoon as the plate voltage of one tube is changed by a change in theconduction of that tube in response to a pulse of predeterminedamplitude, the voltage change is transferred almost instantaneously tothe control grid of the other tube. The conductive condition of thelatter tube is accordingly changed to switch the trigger to its otherstable condition. Since the switching of the trigger from one stablecondition to the other requires only the application of a pulse having acertain amplitude, it is difiicult to obtain reliable trigger operationwhen the trigger is necessarily subjected to various transients capableof switching it from one stable condition to the other.

Accordingly, it is a principal object of the invention to provide anovel trigger circuit which requires a pulse of predetermined minimumamplitude and predetermined minimum duration to effect a switchingthereof.

It is another object to provide a trigger circuit of high stabilitywhich is non-responsive to noise and other unwanted transients.

It is another object to provide a trigger circuit having two tubes andtwo stable conditions alternately assumed wherein a pulse applied to onetube will efiect a switching of the trigger to one stable condition, apulse applied to the other tube will efiect a, switching of the triggerto the other stable condition and pulses applied simultaneously to bothtubes do not affect the stable condition of the trigger.

It is a further object to provide a trigger circuit having two tubes andtwo stable conditions wherein the application of pulses to both tubeswithin a certain predetermined time does not aiTect the stable conditionof the trigger.

It is a further object to provide a trigger circuit having two tubeswherein degenerative feedback is employed to delay the response of thetrigger.

It is a, still further object to provide a trigger circuit having twotubes wherein the plate of each tube is connected solely throughresistance to the control grid of the other,

7 Claims. (01.250-27) V Other objects of the invention will be pointedout in the following description and claims and illustrated in theaccompanying drawings, which disclose, by way of example, the principleof the invention and the best mode, which has been contemplated, ofapplying that principle.

The drawing is a circuit diagram of an embodiment of the novel triggercircuit of the invention.

The arrangement of the trigger circuit will be described with referenceto the values of applied voltage and the values of resistances andcapacitancesused. These values are given solely for the purpose ofclarifying the explanation, and it is to be specifically understood thatthey may be varied considerably without departing from the principles ofthe invention.

Referring more particularly to the drawing, the trigger includes thetubes l0 and H. These tubes may be of the type in which a single tube iscontained in one envelope or of the type wherein the two tubes arecontained in the same envelope such as a 6J6.

The plate of each tube l0 and H is connected to a +150 volt line throughresistors l3 and M in series having values of 12,000 ohms and 7,500ohms, respectively. The cathodes are connected together and through aresistor I5 of 19,700 ohms to a volt line 16. The control grid of thetube I0 is connected through resistors ll and [8 of 1,000 ohms and200,000 ohms, respectively, to the 100 volt line 16. Similarly, thecontrol grid of the tube I l is connected through resistors l9 and 20 of1,000 ohms and 200,000 ohms, respectively, to the line It.

The plate of. the tube i0 is connected through a lead 2!, a resistor 22of 200,000 ohms and the resistor IQ of 1,000 ohms to the control grid ofthe tube H. Similarly, the plate of the tube H is connected through alead 23, a resistor 24 of 200,000. ohms and the resistor ll of 1,000ohms to the control grid of the tube [0. The plate of the tube It! isconnected to its own control grid through a lead 25, a capacitor 26 of0.005 microfarad and the resistor ll. Similarly, the plate of the tubel! is connected to its own control grid through a lead 27, a capacitor28 of 0.005 microfarad and the resistor l9.

Separate input connections are provided for each tube. Input terminal 29is connected through a lead 30 and a resistor 3| of 100,000 ohms to theresistor ll connected to the control grid of the tube l0. Input terminal29 is also connected to the ground or zero voltage line 32,

tive to render the tube conductive.

3 through the lead 30 and a resistor 33 of 5, ohms.

Input terminal 34 is connected through a lead 35 and a resistor 36 of100,000 ohms to the resistor l9 connected to the control grid of thetube ll. Input terminal 34 is also connected to the ground or zerovoltage line 32 through the lead 35 and a resistor 31 of 5,100 ohms.

An output terminal 38 is connected via line 23 directly to the plate oftube I l and the output is taken between terminal 38 and the ground line32.

The two stable conditions of the trigger are designated herein as the onand "off conditions. The trigger is on, when the tube I is conductiveand the tube l l is non-conductive, and the trigger is off when the tubein is nonconductive and the tube H is conductive. For the purposes ofexplanation, the novel trigger is assumed to be initially o (i. e. withtube H conducting) as indicated by the dot to the lower right of thetube l I.

Now a positive pulse may be applied to the input terminal 29 and thevoltage at the control grid of the tube l0 made sufficiently positive torender the tube conductive. As a result, the volt- -age at the plate ofthe tube I0 is decreased and the decreased voltage is transferredthrough the lead 2| and the resistors 22 and 19 to the control grid ofthe tube l l to decrease the conduction of the tube l I. The resultingincreased voltage at the plate of the tube H is transferred through thelead 23 and the resistors 24 and I! to the control grid of the tube ill,to render it still more conductive. This cumulative action is continueduntil the tube l0 reaches a steady state of conduction and the tube llbecomes non-con ductive, to maintain the trigger on.

- Next, a positive pulse may be applied to the input terminal 34 and thevoltage at the control grid of the tube II is thus made sufficientlyposi- The resulting decreased voltage at the plate of the tube H istransferred through the lead 23 and the resistors 24 and I! to thecontrol grid of the tube ID to decrease the conduction of the tube I0.The resulting increased voltage at the plate of the tube I 0 istransferred through the lead 2! and the resistors 22 and H), to thecontrol grid of the tube H to render it still more conductive. Thiscumulative action is continued until the tube ll reaches a steady stateof conduction and the tube it! becomes non-conductive, to maintain thetrigger ofi.

The trigger may be switched from one stable condition to the other, byapplying positive pulses alternately to the input terminals 29 and 34,respectively.

When pulses are applied simultaneously to the control grids of the tubesl0 and l l, the stable condition of the trigger is not changed. Theincreased conduction of the initially conductive tube is utilized tobuck and prevent a change in the stable condition of the trigger. Thisaction is referred to herein as bucking action and the novel triggerarrangement for efiecting it is referred to as a bucking trigger.

To make use of this bucking action, the input terminals 29 and 34 areconnected together or any conventional means may be employed to applypulses to these terminals substantially simultaneously. The mereconnecting together of the terminals causes no change in the stablecondition of the trigger and has substantially no 4 effect on it, sincethe terminals 29 and 34 are at substantially the same voltage.

When a positive pulse is applied simultaneously to the terminals 29 and34, the voltage at the control grids of both tubes Ill and H isincreased and the stable condition of the trigger remains unchangedbecause of the buckin action. The increased voltage on the control gridof the tube ll increases the conduction through that tube and thevoltage at its cathode is increased accordingly. Since the cathode ofthe non-conductive tube I0 is connected to the cathode of the conductivetube II, the voltage on one cathode is the same as that on the other.However, this increased voltage at the cathode of the tube It does notaffect the stable condition of the trigger. Though the voltage on thecontrol grid of the tube I 0 is increased by the pulse applied, it isinsufficient to render the tube l0 conductive because of the increasedVoltage at the cathode. In other words, when pulses are appliedsimultaneously to both tubes of the trigger, the bucking action effectedby the increased current flow through the conductive tube of the triggerprevents conduction through the non-conductive tube and maintains thetrigger in the same stable condition.

The function of the capacitors 26 and 28 connected between the platesand the control grids of the tubes 10 and II, respectively, is extremelyimportant if the pulses applied to the input termi nals 29 and 34 arenot applied exactly simultaneously and bucking action is desired. Thesecapacitors provide a degenerative feedback circuit for the respectivetubes and tend to maintain them in their present conductive state,resisting any change in the stable condition of the trigger. Hence, thecapacitors delay the switching of the trigger from either stablecondition to the other. This delay permits a departure from simultaneityor mistiming in the application of pulses to the terminals 29 and 34without producing a switching of the trigger. The actual departure fromsimultaneity permitted without sacrificing the bucking action describedwill vary with the design of each particular trigger. The triggersdescribed, wherein the capacitors 2E and 28 are each of 0.005microfarad, permits a mistiming in the order of 2,000 microseconds,before the trigger is switched in response to either pulse.

This departure from simultaneity means also that the pulse which willproduce a switching of the trigger must have a duration of at least2,000 microseconds. Hence, pulses having a duration less than 2,000microseconds though of sufficient amplitude to produce a switching ofthe trigger are ineffective to do so because of the degenerativefeedback. It is clear, therefore, that random noise, supply voltagefluctuations and unwanted transients, which happen to be present becauseof the particular circuit arran ement with which the trigger is used, donot produce a switching of the trigger from one stable condition to theother.

From the description it is apparent that the trigger of the invention ispeculiarly useful for producing ordinary triggerin in response to pulsesof predetermined characteristics or as a bucking trigger when pulses arereceived by it simultaneously.

While there have been shown and described and pointed out thefundamental novel features of the invention as applied to a singlemodification, it will be understood that various omissions andsubstitutions and changes in the form and details of the circuitillustrated and in its operation may be made by those skilled in the artwithout departing from the spirit of the invention. It is the intention,therefore, to be limited only as indicated by the scope of the followinclaims.

What is claimed is:

1. A trigger circuit having two grid controlled tubes each including acathode, a grid and a plate, said trigger having two stable conditionsalternately assumed; a resistance of 200K ohms connected from the plateof each tube to the control grid of the other; a connection to thecontrol grid of each tube for switching the trigger from either stablecondition to the other; and a capacitor of 0.005 microfarads connectedfrom the plate to the control grid of each tube for providindegenerative feedback to resist a change in the conductive state of thetube and thereby delay the switchin of the trigger for the order of 2000microseconds.

2. A trigger circuit having two grid controlled tubes each including acathode, a grid and a plate, each trigger having two stable conditionsalternately assumed; a resistive connection from the plate of each tubeto thecontrol grid of the other; a connection to the control grid ofeach tube for switching the trigger from either stable condition to theother; a capacitive connection from the plate to the control grid ofeach tube for resisting a change in the conductive state of the tube; aconductive connection between the cathodes of the tubes so that thevoltage at each cathode is substantially equal to that at the other atall times; and a resistor connecting the cathodes to a source of voltagewhereby the increased conduction through either tube in response to apulse causes an increased voltage at the cathodes rendering the othertube non-responsive to said pulse.

3. In an electronic circuit having two grid controlled tubes eachincluding a cathode, a grid and a plate, said trigger having two stableconditions alternately assumed; a degenerative feedback circuit coupledbetween the plate of each tube and its grid, a purely resistiveconnection between the plate of each tube and the control grid of theother for controlling the conductive state of each tube in accordancewith the plate voltage of the other; and a conductive connection betweenthe cathodes of the two tubes for equalizing the voltages on saidcathodes and for preventing the conduction of one tube when theconduction of the other is increased.

4. A trigger circuit including two grid controlled tubes each includinga cathode, a grid and a plate and each having its plate connectedthrough a load to a positive voltage source said trigger having twoconditions of stability alternately assumed, a resistive connection onlybetween the plate of each tube and the control grid of the other, adegenerative coupling between the plate of each tube and its grid, acommon cathode resistance connecting the cathodes of said tubes to anegative voltage source, a bias resistance between the control grid ofeach tube and said negative voltage source, a first input terminalresistively connected to the control grid of one tube for applyingpositive pulses thereto and resistively connected to a zero voltageline, a second input terminal resistively connected to the control gridof the other tube for applying positive pulses thereto and resistivelyconnected to a zero voltage line whereby the trigger is switched fromeach condition of stability to the other alternately only in response topulses applied alternately to said input terminals.

5. The trigger circuit set forth in claim 4, wherein a capacitiveconnection is provided between the plate of each tube and its controlgrid for resisting a change in the conductive state of the respectivetubes,

6. A bucking trigger circuit having two grid controlled tubes, eachincluding a cathode, a rid and a plate, said trigger having two stableconditions alternately assumed in response to pulses, wherein pulsesapplied simultaneously to an electrode of each tube do not produce achange in the stable condition of the trigger, including a resistiveconnection from the plate of each tube to a grid of the other forcontrolling that grid voltage of each tube in accordance with the platevoltage of the other, a capacitive connection from the plate of eachtube to a grid thereof and means for maintaining voltage equalizationbetween corresponding cathodes of said tubes for preventing a change inthe stable condition of the trigger when pulses are appliedsimultaneously to both tubes, said means including a conductiveconnection between said cathodes.

7. A trigger circuit having two grid controlled tubes each includin acathode, a grid and a plate, said trigger havin two stable conditionsalternately assumed; a purely resistive connection from the plate ofeach tube to the control grid of the other, connections to the contro1grid of each tube for switching the trigger from either stable conditionto the other and a capacitive connection from the plate to the controlgrid of each tube for resisting a change in the conductive state of thetube.

RALPH L. PALMER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,211,750 Humby et al. Aug. 20,1940 2,457,974 Bliss Jan. 4, 1949 2,461,871 Bass Feb. 15, 1949

